1. Field of the Invention
The present invention relates to an image sensor, an image sensor unit and an image reader including a line sensor that carries out reading at the time of illumination of a light source of a respective R, G, B color.
2. Description of the Related Art
As indicated in Japanese Patent Application Laid-open No. 2007-097054, an image reader includes a one-line contact image sensor (CIS) that includes a line sensor in which active picture elements are linearly arranged in one line. In the image reader, a light source of a respective R, G, B color alternatingly illuminates and at the time of illumination of light sources, the one-line CIS reads an image reading medium. On every reading carried out by the line sensor, the one-line CIS generates R data, G data, and B data corresponding to R, G, B colors. In each line cycle, the generated R data, G data, and B data is output as RGB line data to a controller of the image reader. The controller generates image read data from the output RGB line data.
When the one-line sensor reads the image reading medium, the image reading medium moves towards the one-line CIS. Thus, a color of picture elements including the output RGB line data differs from a color of a portion corresponding to the image reading medium because a position of the image reading medium facing the one-line CIS changes at the time of illumination of the light sources. This creates a problem of color shifting. To be specific, the color shifting considerably occurs due to a low reading resolution and a fast moving speed of the image reading medium towards the one-line CIS and also due to significant changes in the position of the image reading medium facing the one-line CIS at the time of illumination of the light sources.
As a method to restrain the color shifting, the image sensor is considered that includes a line sensor in which sensor elements are linearly arranged in three lines. In other words, a three-line CIS is used. However, a three-line CIS is costlier than a one-line CIS. In other words, use of a three-line CIS in an image reader increase the cost of the image reader.
In the image reader using the one-line CIS, once the image reading medium is read using the reading resolution higher than a set reading resolution, the generated image read data can be interpolated in the image read data corresponding to the set reading resolution. However, if the image reading medium is read using the reading resolution higher than the set reading resolution, the moving speed of the image reading medium towards the one-line CIS becomes slower than the moving speed in the set reading resolution. Furthermore, a processing for interpolating the generated image read data in the set reading resolution also takes time. In other words, an image read data generation time, which is a time required till the image read data corresponding to the set reading resolution is generated after the scanning is started by the image sensor, will be lengthened.